Mixers are used in the oil and gas industry to prepare drilling mud, brine, and cement slurry. Jet mixers and vortex mixers are two examples of such mixer designs. Different mixers are generally used for the different products, since the slurries produced and time sensitivity of the slurries are generally different. Moreover, the various components of the slurries may be incompatible; for example, the components of the mud may negatively impact the cement, and even small amounts of the mud chemicals mixed into the cement slurry may result in poor cement performance.
Further, the different slurries may be prepared in different manners. In a mud mixer, for instance, drilling mud is prepared by feeding drilling mud to the jet mixer using a centrifugal pump. This creates a suction effect, so that dry chemical dropped into the hopper is drawn into the gooseneck, mixed with liquid ingredients, and then returned to the mud tank. The supply rate of chemicals in the mixer may be in the range of 100 pounds per minutes when provided manually, or up to 1000 pounds/minute when fed by pneumatic conveyance (e.g., as with barite).
Cement slurry generally contains higher concentration of solid components. In some slurries, the water to cement ratio may be 44% by weight. Also, a large amount of cement is called for to perform a cement job. For example, 100 tons of cement may be employed, yielding more than 150 to 200 tons of slurry. The cement job may be time-sensitive, and may be executed so that the cement hardens at the desired point in the wellbore. Accordingly, cement mixing may be performed “on the fly,” whereby, for example, two tons of cement powder may be poured in the mixer during the mixing period, e.g., in batches for immediate use. A modified jet mixer may be used, in which water is injected in the jet mixer via a centrifugal pump. The slurry may also be injected in the bowl of the mixer allowing recirculation into the mixer for a potential increase of the slurry density. Such slurry injection in the mixer also increases the mixer vacuum effect so that more cement powder can be entrained into the mixing process.